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Only recently have researchers begun to investigate whether barks produced in different contexts vary in their acoustic parameters (such as tone and pitch). Scientists theorized that if— like growls—barks displayed consistent differences, they might have a more specific communicative function, perhaps even be associated with a dog’s internal motivational or emotional state. For example, some barks might convey aggression while others might convey friendliness.

In one early study, Sophia Yin, DVM, MS, recorded a variety of breeds barking in response to different situations: a stranger ringing the doorbell (“disturbance barks”), separated from an owner (“isolation barks”) and play. Yin found that the barks did indeed have different acoustic properties. Disturbance barks were harsher and lower in pitch with little amplitude modulation, while isolation and play barks were pitched higher and had greater tonal and higher frequency and a wider range of amplitude modulation. More recent studies confirm that dog barks follow particular patterns. For example, a dog barking at a stranger sounds very different from a dog barking before going on a walk. But do these vocalizations carry meaning? They do for dogs. When dogs in one study listened to barks recorded in a new context or from a new dog, they gave more attention to the unfamiliar bark. This suggests that dogs can detect that some barks are different from others, though scientists are still exploring ways to determine how exactly they perceive and process that information. Humans, too, can decipher barks. Whether or not they’re experienced with dogs, people are quite good at classifying barks into their appropriate contexts and attributing them to perceived emotional states. After listening to randomly played recordings, people describe isolation barks as full of despair, while barks from a play session are said to be happy. Our ability to do this starts early; by age 10, children are able to assign different-sounding barks to the correct context. Today, we can distinguish the acoustic properties of certain barks so accurately that we’re able to program computers to categorize them (which confirms that computers will one day take over the earth; personally, I hope Ryan Gosling will be there to save us).

Recognizing the Patterns
How do we perceive meaning in the vocalizations of another species ? Apparently, dogs and humans have more in common than a love of shoes. Through their shared mammalian histories, canine and human vocalizations follow similar acoustic patterns. Highpitched and more tonal noises convey friendliness, affiliation and “come here,” whereas low-pitched and less tonal sounds convey aggression and “go away.” These rules and tendencies, which are found across mammalian and avian species, govern our own communication and emotional expression. When talking to infants, we generally use a highpitched “baby” tone rather than lower-register sounds.

A recent publication by Kathryn Lord, PhD, offers an additional take on why dogs bark. She and colleague Ray Coppinger, PhD, investigated the contexts in which other species use barklike sounds: “When other species emit their version of a bark, they are usually in some sort of conf licting situation. For example, an animal is at a nest or den and observes some sort of threat. Customarily, the animal would run, but because of its situation, it can’t, so it barks. We think [that] when dogs bark, they are making these sounds in association with an alert or an internal motivational state of conflict.”

In a sense, Lord and Coppinger argue that “conflicted” should be dogs’ middle name. They suggest that dogs bark in so many different situations because they often find themselves conflicted: they are in the house and want to go out, they are out and want to come in. And it may be that, through the process of domestication itself, dogs have become more prone to put themselves in these sorts of situations. In comparison with wolves, dogs have a substantially decreased f light distance; something can easily get too close before the dog feels conf licted about how to respond.

Julie Hecht, MSc, is a PhD student in Animal Behavior and Comparative Psychology at the Graduate Center, CUNY, and a science writer. She would really like to meet your dog. Follow on Facebook and Twitter @DogSpies.